<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .div1{
            width: 200px;
            height: 200px;
            background-color: red;
        }
        .div1>div{
            width: 100px;
            height: 100px;
            background-color: green;
        }
    </style>
</head>
<body>
    
    <div class="div1">
        <div>
          
        </div>
    </div>

    <script>
        var div1=document.querySelector('.div1');
        div1.addEventListener('mouseenter',function(){
           console.log(111);
        });
    </script>
</body>
</html>